In 1925, after years of civil war, turmoil and foreign intervention, Persia (later called the Kingdom of Iran in 1935) was unified under the rule of Reza Khan, who crowned himself to become Rezā Shāh that same year. Rezā Shāh set on an ambitious program of economic, cultural, and military modernization. Iran, which had been a completely backward,[3] divided, and isolated country under the rule of the Qajar Dynasty, was now rapidly evolving into a modern industrial state. Rezā Shāh also made many improvements, such as building infrastructure, expanding cities and transportation networks, and establishing schools.[4]

Rezā Shāh also set forth on a policy of neutrality. But in order to help finance and support his ambitious modernization projects, he needed the help of the west.[2][4]

For many decades, Iran and the German Empire had cultivated ties, partly as a counter to the imperial ambitions of Britain and the Russian Empire (and later, the Soviet Union). Trading with Germany appealed to Iran because the Germans did not have a history of imperialism in the region, unlike the British and Russians.[2][4] When the Nazis took over Germany in 1933, trade was not seriously affected. While Nazi propaganda sometimes tried to play up the similarities between the two Aryan nations, in reality Iran cared little for the Nazis' policies, including anti-Semitism. An example of this was when Iran's embassies in occupied European capitals rescued over 1,500 Jews and secretly granted them Iranian citizenship, allowing them to move to Iran.[2]

Nevertheless, British propaganda began to accuse Iran of supporting Nazism and being pro-German.[2]

Although Rezā Shāh declared neutrality at an early stage of World War II, Iran assumed greater strategic importance to the British government, which feared that the AbadanOil Refinery, owned by the UK-owned Anglo-Iranian Oil Company, might fall into German hands; the refinery produced eight million tons of oil in 1940 and was thus a crucial part of the Allied war effort.[2][5] Tensions with Iran had been already strained since 1931 when Rezā Shāh cancelled the D'Arcy Concession, which gave the Anglo-Iranian Oil Company the exclusive right to sell Iranian oil, with Iran receiving only 10% (possibly 16%)[6] of the profits.[2][4]

Following Germany's invasion of the USSR in June 1941, Britain and the Soviet Union became formal Allies, providing further impetus for an Allied invasion.[7] With the German Army steadily advancing through the Soviet Union, the "Persian Corridor" formed by the Trans-Iranian Railway was one of the easiest ways for the Allies to get desperately needed Lend-Lease supplies to the Soviets, by sea from the United States. British and Soviet planners began to see the vital importance of that railway, and sought to secure it into their hands. As increasing U-boat attacks and poor ice conditions made convoys to Arkhangelsk extremely dangerous, the railway became an increasingly attractive route. In addition, the Soviets wanted to make Iranian Azerbaijan and the Turkmen Sahra part of the Soviet Union, and possibly turn Iran into a communist state. The two Allied nations applied pressure on Iran and the Shah, but this led only to increased tensions and anti-British rallies in Tehran. British propaganda described these protests as being "pro-German".[2][4]

Demands from the Allies for the expulsion of German residents in Iran (mostly workers and diplomats) were also refused by the Shah; a British embassy report in 1940 estimated that there were almost 1,000 German nationals in Iran.[8] According to Iran's Ettelaat newspaper, there were actually 690 German nationals in Iran (out of a total of 4,630 foreign nationals, including 2,590 British).[9] However, the Iranians also began to reduce their trade with the Germans under Allied demands.[2][4] Rezā Shāh sought to remain neutral and anger neither side, yet this was becoming increasingly difficult with the British/Soviet demands on Iran. The British forces were already present in sizeable numbers in Iraq as a result of the Anglo-Iraqi War earlier in 1941. Thus, British troops were stationed on the western border of Iran prior to the invasion.

The Iranian warship Babr (Tiger) after being shelled by the British sloop HMS Shoreham, during the surprise attack on Iran, August 1941.[10] The Babr was later sunk by the Australian sloop HMAS Yarra.

The invasion was an undeclared surprise attack, described by Allied forces as rapid and conducted with ease.[10] Prior to the invasion, two diplomatic notes were delivered to the Iranian government on 19 July and 17 August requiring the Iranian government to expel German nationals.[11] The second of the notes was recognised by the prime minister Ali Mansur as a disguised ultimatum.[12][13]General Wavell later wrote in his despatch, "...it was apparent that the Iranian Government fully expected an early British advance into Khuzistan and that reinforcements, including light and medium tanks, were being sent to Ahvaz."[14][15]

Soviet and Indian soldiers meet in late August.

Following the invasion, Iran summoned Sir Reader Bullard and Andrey Andreyevich Smirnov, the British and Soviet ambassadors to Iran. The Shah demanded to know why they were invading his country and why they had not declared war; both answered that it was because of "German residents" in Iran. When the Shah asked if the Allies would stop their attack if he expelled the Germans, the ambassadors did not answer. The Shah sent a telegram to President Roosevelt of the United States, pleading with him to stop the invasion. As the then-neutral United States had nothing to do with the attack, Roosevelt was not able to grant the Shah's plea, but stated that in his opinion the "territorial integrity" of Iran should be respected.[2][4]

The invading Allies had 200,000 troops overall, in addition to modern aircraft, tanks, and artillery.[16]

In response to the invasion, the Iranian Army mobilised nine infantry divisions, some of them motorized. Two of the divisions also had tanks. Their military had a standing force of 126,000–200,000 men. While Iran had taken numerous steps through the previous decade to strengthen, standardize, and create a modern army, they did not have enough training, armour, and air power to fight a multi-front war. Rezā Shāh had modernized Iran's military, but his modernizations had not been completed by the time war broke out[2] and the Iranian Army had been more focused on internal security operations than on resisting external invasions.[17]

Iran was self-sufficient in the manufacture of small arms. Iran had bought 100 FT-6, and Panzer 38(t)light tanks, and additional La France TK-6 armoured cars, enough to outfit their 1st and 2nd division.[18] Further Iranian orders had been delayed by World War II.[19] While it was a large order, and they were excellent tanks, they were not enough to fight back a multi-front invasion by two great powers. The Imperial Iranian Air Force also consisted of 150-200 HawkerAudax, Hind, and Fury aircraft of various models, some being made under license in Iran, and having their pilots trained in Europe. However despite their recent purchase, due to the changing nature of air warfare in the 1930s, all but 50 of them would be obsolete when the invasion began. Prior to the attack, the Royal Air Force dropped leaflets on Iranian troops, asking them to not fight and to understand their country was "not threatened" as it was being "liberated" from possible Nazi destruction. [16]

The Iranians had little time to organize an effective defense, as the Allies achieved a tactical surprise.[2]

Soviet and British soldiers rendezvous near Qazvin.

The war began in the early morning hours of 25 August, when Royal Air Force aircraft entered Iranian airspace. They bombed targets in the cities of Tehran and Qazvin and various other towns, and also dropped leaflets urging the Iranians to surrender. The Soviets bombed targets in cities such as Tabriz, Ardabil, and Rasht. Civilian and residential areas were hit, and several hundred people were killed and wounded.[2][16] Rezā Shāh refused requests by his generals to destroy the road and transportation networks, largely because he did not want to damage the infrastructure that he had painstakingly built during his reign. This contributed to the speedy victory of the allies.[2]

Without any military allies able to come to its assistance, Iranian resistance was rapidly overwhelmed and neutralised by Soviet and British tanks and infantry. The British and Soviet forces met at Sanandaj (called Senna by the British) (160 kilometres (100 mi) west of Hamadan) and Qazvin (called Kazvin by the British) (160 kilometres (100 mi) west of Tehran and 320 kilometres (200 mi) northeast of Hamadan) on 30 and 31 August respectively.[2][16] Faced with massive defeats, the Shah ordered his military to stop fighting and stand down on 29 August, 4 days into the invasion.[2]

The campaign began on 25 August with a dawn attack by the British sloop HMS Shoreham with several other Royal Navy and Royal Australian Navy craft on the harbour at Abadan. The Iranian sloop Palang and Babr were quickly sunk, and remaining ships were destroyed or captured. There had been no time to prepare resistance, as the Iranians had been taken completely by surprise. Most of the Iranian navy was destroyed without even time to act, and the head of the navy AdmiralGholamali Bayandor was killed.[2]

The petroleum installations at Abadan were of vital importance to the British commanders, as well as keeping the employees of the Anglo-Iranian Oil Company safe from possible reprisals. Khuzestan province was defended by 27,000 troops from the 1st, 2nd, 6th and 16th infantry divisions, consisting of both light and mechanized infantry. All Iranian tanks were deployed in Khuzestan as part of the 1st and 2nd divisions.[19] A British naval and paratrooper landing force landed at Abadan securing the city and the refinery.[16] The Iranians managed to put up a resistance, and the refinery and the city were captured after hand to hand combat resulting in the deaths of several British and Indian troops.

Persian Gulf Command map showing position of posts and stations.

The Iranians were completely taken by surprise, and there was virtually no resistance in other areas of Khuzestan. Meanwhile, Bandar Shahpur (now named Bandar Khomeini, after Iran's later revolutionary leader, Ruhollah Khomeini) was captured by two battalions from 8th Indian Division's 24th Indian Brigade making an amphibious landing from the Australian armed merchant cruiserHMAS Kanimbla to secure the port and petroleum terminal there. The Royal Air Force attacked airbases and communications, and rapidly gained air superiority. They destroyed numerous Iranian aircraft on the ground, and protected their forces from Iranian counterattacks. T[16]

The 8th Indian Division (18th Brigade plus 25th Brigade under command from 10th Indian Division) advanced from Basra towards Qasr Sheikh (which was taken on 25 August) across the Shatt-al-Arab waterway and captured the city of Khorramshahr, which was next to Abadan on the same day. The Karun River was not secured, as Iranian snipers remained, impeding British advance for a short time. Britain also landed troops at Bandar Abbas as well. The Shatt-al-Arab was secured. By 26 August, there was no organized resistance remaining in the area, with the Iranian forces overwhelmed by superior firepower, and 350 Iranians taken prisoner, and many killed or scattered. Other Iranians surrendered as well.[16]

The British hoped to capture Ahvaz and then drive north into Zagros Mountains passes to reach Qazvin, where they would link up with British troops in central Iran, and Soviet troops from the north. By early morning at 27 August, the British forces had reached Ahvaz.[2] However, the Iranians led by General Mohammad Shahbakhti had prepared a strong defense. Iranian infantry had entrenched themselves around the city, with artillery support and tanks. Although Iranians had taken heavy losses and their morale was decreasing, they were prepared to fight hard. The Indian Army advance came to a halt and they were hesitant to attack to cross the Karun River and attack the city. A British attack on the defenses around the city were repelled by Iranian tanks and infantry.[2]

Whether the Iranian defense could have been successful is debatable. However, on 29 August, after some more sporadic fighting, word reached the Iranian commanders at Ahvaz that their government had accepted a ceasefire, and that they were not to fight any longer.[2] The British and Iranians agreed as part of the ceasefire that the Iranians would not lay down their arms and remain at their posts, but they would be joined by the British troops who would carry out a parade in the city. In exchange, the Iranians would safely evacuate British residents in the city to British troops. The British with their Indian troops paraded in the city, with full military honors given by the Iranian general.[16]

Farther north, the 10th Indian Infantry Division[20] under Major-General William Slim attacked central Iran. Slim directed remotely the battle via radio from India. The Indian Army infantry and armour massed at the Iraqi border town of Khanaqin (160 kilometres (100 mi) northeast of Baghdad and 480 kilometres (300 mi) from Basra). Unlike the terrain in Khuzestan, the British were attacking in Kermanshah province, with mountainous terrain. They would be forced to go on steep mountain passes along a narrow road.[16]

The British force broke through the border at the town of Qasr-e Shirin and moved into the Naft Shahr oilfield with little opposition. The British stated that the operation had been carried out with minimum losses for the Iranians. However, British troops faced heavy opposition by 2,000 Iranians as they tried to capture the town of Gilan-e-Gharb 30 kilometres (20 mi) inside of Iran, which if successful would block the British from moving through the steep mountain pass.[16] It was called in Iran the Pai Tak Pass. The RAF provided close air support for their troops, and was involved in several dogfights with Iranian aircraft. They took no losses, while 6 Iranian fighters were shot down and several others damaged, ensuring their air superiority. They also bombed several local towns and dropped leaflets urging surrender.

The British captured Gilan-e-Gharb and attacked Iranian forces who desperately defended the town of Sarpol-e-Zahab[16] With overwhelming firepower, and decreasing Iranian morale, the Iranians did not stand a chance and the British captured that town as well, scattering the remaining defenders. The Pai Tak Pass, and the road to Kermanshah and eventually Tehran was open. The armoured columns began to secure the pass and the areas around it.[16]

The British forces moved along the Kermanshah highway towards the city of Shahabad (now Islamabad-e-gharb). There was little Iranian resistance, however they did cut down some trees and even dynamited a section of the road, delaying the British forces for hours.[16]

The main Iranian forces in the region consisted of the 5th and 12th infantry divisions of 30,000 troops with supporting artillery at Kermanshah and Sanandaj. They were all light infantry (as the mechanized and armour had been stretched thin fighting on multiple fronts). The chances that they could have defended against the British were low. The British had reached the outskirts of Shahabad in the early morning hours of 28 August after suffering multiple delays. Here at the village of Zibri they faced a strong Iranian garrison willing to put up a fight. The British took multiple casualties, but with poor Iranian leadership and overwhelming British firepower, they were cleared out rapidly. The British took Shahabad on the morning of the same day.[16]

By 29 August, the British had reached the town of Kerend, and were within 3 kilometres (2 mi) of Kermanshah and were preparing for their attack on the city. At this point, the Iranian commanders were informed by their government that they had received a ceasefire order, and were ordered to stand down. They declared Kermanshah an open city and the British entered the city on 1 September. They also entered Sanandaj peacefully and eventually Qazvin as well, the latter which had already been captured by the Red Army.[16]

The Soviet forces attacked on 25 August. Iranian airbases were destroyed by preliminary air attacks. The Soviets attacked using three armoured spearheads, totalling over 1,000 tanks and motorized infantry (the Iranians had no tanks in the area).[2] The first force, consisting of the 47th Army[20] broke through the border and moved from the Azerbaijan SSR into Iranian Azerbaijan. They moved towards Tabriz and Lake Urmia. They captured the Iranian city of Jolfa. An Iranian reconnaissance aircraft discovered the forces south of Jolfa moving towards Marand. It was possible for the Iranian 3rd Division under General Matboodi to move motorized infantry towards Shibli in order to halt the breakthrough, but due to being taken by surprise, he failed to make the proper counterattack. He also failed to destroy the bridges and highways with explosives, allowing the Soviets to rapidly move through the region.[2] Five Iranian bombers were intercepted trying to attack the Soviet positions around Jolfa.[16]

Meanwhile, the 53rd Army crossed the border[20] and moved towards the city of Ardabil, defended by Iran's 15th Division led by Brigadier-General Qaderi. Two Iranian regiments began to move towards the town of Nir to confront the invaders. Despite having a solid force and well-motivated troops, General Qaderi jumped into his car and abandoned his troops. He even sabotaged the defense even further by ordering the supply trucks delivering food, weapons, and artillery to unload their weapons to make way for his personal belongings. The Soviets bypassed Nir and moved south.[2] Ardabil was bombed by the Soviet Air Force, and received minor damage to its barracks. Cut off and bypassed, both the Iranian 15th Division in Ardabil and the 3rd Division in Tabriz began to collapse. Despite that, the regular troops tried to maintain order, and began to march towards the enemy without many of their commanders. However, lacking food, supplies, and ammunition, the troops were forced to abandon much of their heavy equipment. Heavy pockets of resistance remained, with some desperate fighting until the end. They were unsurprisingly beaten by the Soviets, who 26 August had occupied Iranian Azerbaijan (including Tabriz and Ardabil).[2]

On 25 August, the Soviet attack against Gilan Province began with their Caspian Sea Flotilla, led by Rear-Admiral Sedelnikov. The flotilla consisted of more than a dozen patrol boats, destroyers, multiple anti-aircraftbarges and landing craft. Facing them were three Iranian gunboats. Meanwhile, the 44th Army crossed the border and moved into Gilan Province. They moved along the Astara highway and the main coastal highway (Jadeh-e-Shomal). Due to heavy Iranian forces in the area, the naval landing force would secure Iranian cities, and then be joined by the land forces. The flotilla landed troops and rapidly captured the border city of Astara. The landing force boarded their ships and moved towards their next targets.[2]

The main objective of the attack was to capture Iran's Caspian Sea port of Bandar Pahlavi (today Bandar Anzali). The Iranian forces in Gilan, led by General Iranpour, made their stand at the provincial capital of Rasht and Bandar Pahlavi, and offered a stubborn resistance.[16] The Iranian forces sank barges at the entrance to Pahlavi harbor, and lacking coastal artillery, moved a battery of 75mm guns to the area. The Iranians fought desperately, and despite Soviet superiority, the Iranians prevented them from landing. The Iranians were careful to not fire their guns while Soviet aircraft flew overhead, preventing them from disclosing their location. Soviet aircraft were kept at bay by 47mm anti-aircraft artillery on Iranian barges.[2]

The next day however, the Soviet Air Force moved into action, using many heavy bombers. In groups of 4 aircraft each, their bombers attacked military positions and civilian targets throughout Gilan, including Bandar Pahlavi and Rasht. At least 200 civilians were killed during the bombings. The bombings also destroyed many Iranian positions, and resistance was finally crushed by the 44th army advancing from land, capturing both cities. Fighting was very intense, and the Soviets took their heaviest casualties of the invasion here. However, lacking armour and air power, the Iranians could not stop the enemy.[2][16] On 28 August, they were forced to surrender. Nevertheless, some Iranian forces refused to accept defeat, and retreated to Ramsar to continue fighting. Their efforts were undercut when the Iranian government announced a ceasefire the next day.[2] By that time, the Soviet forces had reached the city of Chalus, meaning that they could cross the Chalus Highway (Jadeh-e-Chalus) and reach Tehran across the Alborz Mountains.[16]

Meanwhile, the Soviet invasion force in Iranian Azerbaijan had moved south. The 47th Army[20] had been delayed in the Jolfa area when three individual Iranian soldiers managed to block an important bridge until they ran out of ammunition and were killed. The Soviets did not use artillery lest they damage the bridge and delay their advance further.[9] The 47th Army moved south, first capturing Dilman (100 kilometres (80 mi) west of Tabriz), and capturing the city of Urmia (Oromiyeh), ostensibly to block the escape of "German agents". Urmia (Orumiyeh) was defended by only a few snipers. The Soviets responded by bombing targets in the city, killing over a dozen people and wounding many others, and much of the city's bazaar was burned.

Meanwhile, the 53rd Army[20] moved south of Ardebil towards the Tehran-Karaj-Tabriz highway, capturing the city of Meyaneh (Mianeh) and moving southeast towards Qazvin and Tehran by 27–28 August.[16] Iran's 15th and 3rd divisions had already been bypassed and defeated, and there was only sporadic resistance against the Soviets. The Soviet armoured spearhead drove down the highway, and poised to take Qazvin on the 29th (151 kilometres (94 mi) from Tehran), followed by Saveh and Qom, south of Tehran (cutting the main Tehran-Saveh-Persian Gulf highway and cutting Iran effectively in two. But the Iranians accepted the ceasefire on 29 August, and the Soviets entered the now "open city" on 30 August. At the same time, elements of the 53rd Army captured the city of Hamadan. One civilian (a small child) was killed in a small bombing raid, and the sporadic resistance was defeated. They stopped their advance on 1 September and did not move further towards Tehran from Qazvin in light of negotiations with Iran's government.[16]

On 25 August, the Soviet Army invaded northeastern Iran from the TurkmenistanSSR. Details of this invasion were not nearly as extensive as details of the others. The Soviet invasion force had to cross mountainous terrain, and its goals were to recruit new troops from the Turkmen Sahra, assemble with the Soviet troops and to capture the city of Mashhad, the second largest city in Iran.[16]

Defending Mashhad and Khorasan province was Iran's 9th infantry division, totaling 8,000 troops. They were light infantry, and it was unlikely that they could defend against the more numerous Soviet forces with armour and air power. The Soviet Air Force bombed Mashhad Airport, destroying many Iranian fighter aircraft, along with numerous military barracks. The Soviet forces advanced in three columns across the border. There was heavy fighting for three days, and by 28 August, the Iranians had been driven back after taking heavy casualties. Mashhad fell to the Soviets the same day.[16]

...on the basis of the declarations which Your Excellency has made several times regarding the necessity of defending principles of international justice and the right of peoples to liberty. I beg Your Excellency to take efficacious and urgent humanitarian steps to put an end to these acts of aggression. This incident brings into war a neutral and pacific country which has had no other care than the safeguarding of tranquillity and the reform of the country." — a letter of 25 August[citation needed]

However, this plea failed to prompt a response from the US President to prevent the invasion of Iran, as Roosevelt's response shows:

Viewing the question in its entirety involves not only the vital questions to which Your Imperial Majesty refers, but other basic considerations arising from Hitler's ambition of world conquest. It is certain that movements of conquest by Germany will continue and will extend beyond Europe to Asia, Africa, and even to the Americas, unless they are stopped by military force. It is equally certain that those countries which desire to maintain their independence must engage in a great common effort if they are not to be engulfed one by one as has already happened to a large number of countries in Europe. In recognition of these truths, the Government and people of the United States of America, as is well known, are not only building up the defenses of this country with all possible speed, but they have also entered upon a very extensive program of material assistance to those countries which are actively engaged in resisting German ambition for world domination.[citation needed]

Roosevelt also reassured the Shah by noting "the statements to the Iranian Government by the British and Soviet Governments that they have no designs on the independence or territorial integrity of Iran". However, in 1945, the Soviets would be responsible for backing two breakaway territories in the north.

British and Soviet officers inspect troops, in preparations to the Joint Russo-British military parade in Tehran. Iran, September 1941

By 28–29 August, the Iranian military situation was in complete chaos. The Allies had complete air supremacy over the skies of Iran, and large sections of the country were in their hands. Major Iranian cities (such as Tehran) were suffering repeated air raids. In Tehran itself, the casualties had been light, but the Soviet Air Force dropped leaflets over city, warning the population of an upcoming massive bombing raid, and urging them to surrender before suffering imminent destruction.[21] Tehran's water and food supply had faced shortages, and soldiers fled in fear of the Soviets killing them upon capture (similar to the Katyn Massacre). Faced with total collapse, the royal family (except the Shah and the Crown Prince) fled to Isfahan.[2][21][21]

The collapse of the army that Rezā Shāh had spent so much time and effort creating was humiliating. Many of the military generals had behaved incompetently, or were secretly sympathizing with the British and ended up sabotaging the Iranian resistance.[2] The army generals met in secret to discuss surrender options. When the Shah learned of the generals' actions, he beat the head of the armed forces General Ahmad Nakhjavan with a cane, and physically stripped him of his rank. He was nearly shot by the Shah on the spot, but at the insistence of the Crown Prince, he was sent to prison instead.[21] The Shah ordered the resignation of the pro-British Prime MinisterAli Mansur, whom he blamed for demoralizing the military.[21] He was replaced with Mohammad Ali Foroughi, a former prime minister.[2] The Shah ordered the Iranian military to end resistance and stand down and order a ceasefire. He entered into negotiations with the British and Soviets.[2][21][21]

However, the new prime minister Foroughi was an enemy of Rezā Shāh (he was forced into retirement in earlier years for political reasons, and his son was executed by firing squad). When he entered into negotiations with the British, instead of a negotiating a favorable settlement, Foroughi implied that both he and the Iranian people wanted to be "liberated" from the Shah's rule.[21]

The British and Foroughi agreed that in order for the Allies to withdraw from Iran, the Iranians would have to assure that: the German Minister and his staff should leave Tehran, that the German, Italian, Hungarian and Romanian legations should close, and that all remaining German nationals (including all families) be handed over to the British and Soviet authorities. The last order would mean almost certain imprisonment or (in the case of those handed to the Soviets) possible death. Rezā Shāh delayed on the last demand. Instead, he planned the secret evacuation of all German nationals from Iran. By 18 September, most of the German nationals had escaped via the Turkish border.[9]

In response to the Shah's defiance, the Red Army on 16 September moved to occupy Tehran. Fearing execution by the communists, many people (especially the wealthy) fled the city. Rezā Shāh, in a letter hand written by Foroughi, announced his abdication, as the Soviets entered the city on 17 September. The British wanted to restore the Qajar Dynasty to power, because they had served British interests well prior to Rezā Shāh's reign. But the heir to the throne, Hamid Hassan Mirza, was a British citizen who spoke no Persian. Instead (with the help of Foroughi), Crown PrinceMohammad Reza Pahlavi took the oath to become the Shah of Iran.[21] Rezā Shāh was arrested before he was able to leave Tehran, and placed into British custody. He was sent to exile as a British prisoner in South Africa, where he died in 1944.[2][4] The Allies withdrew from Tehran on 17 October. However, Iran was effectively divided between Britain and the Soviet Union for the duration of the global war, with the Soviets stationed in northern Iran, and the British not moving beyond Hamadan and Qazvin.

Lend-Lease Program U.S. planes stand ready to be picked up at Abadan Air Field, Iran.[22]

A picture of a mechanical workshop belonging to the British Army which was tasked to repair and provide service for the Soviet Army's trucks.[23]

With this crucial supply route now open to the Soviet Union, the so-called Persian Corridor would provide a massive flow of supplies (over 5 million tons of materiel) to the Soviets primarily, but also the British in the Middle East.

In the end of August 1942, German intelligence agents spread propaganda leaflets in Tabriz as well as other cities. Furthermore an underground fascist organisation, Melnune Iran, was founded. Agents of Melnune Iran instigated anti-government protests in the lake Urmia region. Bakhtiari and Qashqai tribes showcased armed resistance against the new government.[24]

The new Shah signed a Treaty of Alliance with Britain and the Soviet Union in January 1942, under which Iran provided nonmilitary assistance to the Allied war effort. Article Five of this treaty, although not entirely trusted by the Iranian leader, committed the Allies to leaving Iran "not more than six months after the cessation of hostilities". In September 1943, Iran declared war on Germany, thus qualifying for membership in the United Nations. At the Tehran Conference in November of that year, US President Franklin D. Roosevelt, British Prime MinisterWinston Churchill, and General Secretary Joseph Stalin reaffirmed their commitment to Iran's independence and territorial integrity and displayed a willingness to extend economic assistance to Iran. The treaty ruled that Iran was not considered to be "occupied" by the Allies, but instead a member of the Allied Powers.[4]

The effects of the war, however, were very disruptive for Iran. Much of the government's bureaucracy had been damaged by the invasion, and food and other essential items were scarce.[25] To make matters worse, the Soviets appropriated most of the harvest in northern Iran, leading to food shortages for the general public. The British and Soviet occupiers used the delivery of grain as a bargaining chip, in addition the food crisis was exacerbated because of foreign troops who needed to eat, and the use of the transportation network to move military equipment. The British pressured the Shah to appoint Ahmad Qavam to be prime minister, who proceeded to mismanage the entire food supply and economy. In 1942, bread riots took place in Tehran. Martial law was declared and several rioters were killed by the police. In addition, inflation increased by 450 percent, imposing great hardship on the lower and middle classes. In some areas, famine occurred, leading to loss of life.[4] Nevertheless, there was virtually no armed resistance against the occupiers during their time in Iran.

In 1943, American troops joined the Allied forces in Iran. 30,000 Americans helped to man the Persian Corridor. 26–34% of the supplies sent to the USSR under the Lend-Lease Act were sent through Iran. The Americans also assuaged Iranian fears of colonization by the two powers by confirming that they would respect the independence of Iran. The US also extended Lend-Lease assistance to Iran, and to train the Iranian army. Arthur Millspaugh became the finance minister of Iran but ran into much opposition trying to direct Iranian finances.[4]

There were two notable German attempts to undertake operations against the Allies in 1943. In the summer of 1943, Abwehr's Operation Francois was an attempt to use the dissident Qashqai people in Iran to sabotage British and American supplies bound for the Soviet Union. Also in 1943, Operation Long Jump was an unsuccessful German plot to assassinate the "Big Three" Allied leaders, Joseph Stalin, Winston Churchill, and Franklin Roosevelt, at the Tehran Conference.

1950's era Iranian postage stamp illustrating the Iranian warship Palang (Leopard). The British Royal Navy sank the Palang while it was moored at an Abadan pier during the surprise attack on Iran in August 1941.[10]

During the three years of occupation, Joseph Stalin had expanded Soviet political influence in Azerbaijan and the Kurdish area in northwestern Iran, as well as in Iran founding the communist Tudeh Party of Iran. The Soviets had attempted during their occupation to stir tensions between the tenant-farmers and the landlords (known in Iran as arbabs).[16] On 12 December 1945, after weeks of violent clashes a Soviet-backed separatist People's Republic of Azerbaijan was founded. The Kurdish People's Republic was also established in late 1945. Iranian government troops sent to reestablish control were blocked by Soviet Red Army units.

When the deadline for withdrawal arrived on 2 March 1946, six months after the end of World War II hostilities, the British began to withdraw, but Moscow refused, citing "threats to Soviet security."

Soviet troops did not withdraw from Iran proper until May 1946, following Iran's official complaint to the newly formed United Nations Security Council, which became the first complaint filed by a country in the U.N.'s history, and a test for the UN's effectiveness in resolving global issues in the aftermath of World War II. However, the UNSC took no direct steps to pressure the Soviets to withdraw.[26]